CSC professor returning to West Nile Fever study

Again this summer, Dr. Lawson and several CSC students will collect mosquitoes and birds in Dawes, Sheridan and Sioux counties as part of a statewide effort headed by the Nebraska Health and Human Services System. CSC laboratories also will be used to sort mosquitoes that are collected at North Platte, Ogallala, Scottsbluff and Valentine.

Culex mosquitoes, which are the carriers of WNF, will be sent to a laboratory at the University of Nebraska Medical Center in Omaha to determine if they test positive.Last summer, both mosquitoes and birds collected from each of the three northwest counties tested positive.

In 2003, Nebraska was second only to Colorado in the number of WNF cases. There were 2,307 confirmed cases compared to 174 in 2002. Also, there were 29 deaths attributed to the syndrome last year compared to eight the previous year.

“We want to thank the people who cooperated with our study last summer and hope they’ll help us again this year,” said Lawson. “We still have a lot of unanswered questions concerning West Nile. It is a serious situation. Scientists throughout the state and the nation are working hard to get information that will help deal with the problem.”

Last year, Lawson said about a third of the approximately 1,000 samples of mosquitoes that he and his helpers sent to Omaha tested positive for WNF. Approximately 50 culex mosquitoes are placed in each plastic vile that is frozen, packed in dry ice and mailed. About half of the 31 birds that were collected in the three counties last year also tested positive.

This year, as soon as two birds from a county have tested positive, no more will be tested, although records will continue to be kept. Three species of birds have been identified as the primary carriers. They are crows, blue jays and magpies. Anyone finding one of these birds dead is asked to contact Lawson by email at rlawson@csc.edu or by telephone at 308-432-6298.

It is also believed that owls and hawks may be carriers. Lawson said anyone finding one of these birds dead should contact him, and anyone seeing one of these birds acting strange should call a conservation officer. As members of the raptor family, they cannot legally be taken by the average citizen.

Culex mosquitoes generally do not appear until about mid-summer, although the first case of WNF was reported in eastern Nebraska on June 11 last year. Culex mosquitoes initially bite a bird that is infected and then transmit WNF when they bite humans.

Lawson will set out mosquito traps in the three counties around June 1. He said one trap often catches 1,000 to 2,000 mosquitoes overnight. A majority of the mosquitoes will be a species of floodwater mosquito, which is not a carrier. By using a microscope, Lawson and his student assistants can determine the species of the mosquitoes, sort out the culex and send them to Omaha.

Lawson said moisture conditions apparently don’t affect culex population.

“If we have a wet year, we’ll have maybe 10 times more floodwater mosquitoes than we’ll have during a dry year,” the CSC professor said. “But we seem to have about the same number of culex regardless of the weather.”

About the only good news concerning West Nile Fever, Lawson said, is that humans apparently get the infection only once. He suspects that numerous individuals in northwest Nebraska have had WNF, probably have not known it, and are no longer susceptible. However, no one should take that chance and not use a repellant when going outdoors, particularly in July, August and September, or until the first hard freeze occurs.

The repellant should contain Deet, Lawson said. He said brands containing 30 percent Deet are the most effective. Other brands with lesser amounts of Deet are “more user-friendly,” but must be applied more frequently to be effective.

Older people are most susceptible to WNF. Last year in Nebraska, the average age of the diagnosed patients was 44. The 29 who died ranged from 50 to 97 years with the average age 80.

Symptoms include fatigue, malaise, anorexia, nausea, vomiting, eye pain and a headache. There is no known treatment, but rest and possibly hospitalization are recommended.

Horses apparently are the only mammals other than humans who are susceptible to WNF, but they can be vaccinated for it while humans cannot. In 2002, more than 300 horses died of WNF in the state. Last year, while the number of human cases skyrocketed, the number of horses afflicted declined, possibly because many of them were vaccinated.

Chadron veterinary John Gamby said he doesn’t know what percentage of the horses locally have been vaccinated this year, but he is certain not all of them will be.

If horses have been vaccinated previously, the shots cost $15 for WNF. The charge is $21.50 if the serum also covers sleeping sickness. Horses that have not previously been vaccinated need to have two shots the first year.